It is well known, particularly in the field of transporting and using particulate materials, commonly powders, granules, pellets, and the like, that it is important to keep product particles as free as possible of contaminants. Particulates are usually transported within a facility where they are to be mixed, packaged or used in a pressurized tubular system that in reality produces a stream of material that behaves somewhat like a fluid. As these materials move through the pipes, considerable friction is generated not only among the particles themselves, but also between the tube walls and the particles in the stream. In turn, this friction results in the development of particle dust, broken particles, fluff, streamers (ribbon-like elements that can “grow” into quite long and tangled), glass fibers in glass filled products, that can impede the flow of materials. The characteristics of such a transport system are quite well known, as is the importance and value of keeping product particles as free as possible of contaminants.
The term “contaminant” as used herein includes a broad range of foreign material and includes foreign material as well as broken particles or streamers of the product being transported. The generation of contaminants, also referred to as dust, including microdust, can be from a large number of sources, including, in the way of examples, the creation of dust particles during the processing of plastic pellets in which the larger particles are segregated to be re-ground; organic matter in food grains, such as shells and hulls; the creation of dust in the formation of iron ore pellets; and, as noted previously, the mere conveyance of the pellets in pipes and other mechanical conveying and handling systems. Using plastics as an example, such foreign material could have a detrimental effect on the finished product. Specifically, foreign material different in composition from the primary material, such as dust, and non uniform material of the primary product, such as streamers, would not necessarily have the same melting temperatures as the primary product and would cause flaws when the plastics material is melted and molded. Furthermore, streamers can impact the weighing scale and plug the dosing screws at bagging stations.
Considering product quality, and focusing on moldable plastics as a primary example, foreign material different in composition from the primary material, such as dust, non-uniform material of the primary product, fluff, and streamers, does not necessarily have the same melting temperatures as the primary product and causes flaws when the material is melted and molded. These flaws result in finished products that are not uniform in color, may contain bubbles, and often appear to be blemished or stained, and are, therefore, unsellable. It is important to note that since these same non-uniform materials often do not melt at the same temperature as the primary product, the unmelted contaminants cause friction and premature wear to the molding machines, resulting in downtime, lost production, reduced productivity, increased maintenance and thus increased overall production costs.
Since dust and other contaminants are generated mostly by the transport system, it is of primary importance to not only provide apparatus for thoroughly cleaning the particles, but to do so as close to the point of use of the particles as possible so as to avoid the generation of contaminants through additional transport. Accordingly, compact dedusters have been used for many years to clean materials in this application, capable of handling smaller volumes of product, yet also capable of thoroughly cleaning the product. The compact dedusters permit the installation of the deduster immediately before final use of the products, such as being installed directly on top of molding machines or extruders, or on top of silos, as well as under silos, before packaging and bagging, rather than at an earlier stage after which re-contamination can occur before the products are utilized. Of course, the dedusters can be installed as a free standing unit, as well.
Dedusters used to clean contaminants from particulate material can be found in U.S. Pat. No. 5,035,331, granted to Jerome I. Paulson on Jul. 30, 1991, in which air is blown upwardly through wash decks over which a flow of contaminated particulate material is passed so that the flow of air up through the wash decks removes the contaminants from the material flow. A magnetic field is provided by the deduster so that the particulate material flow passes through the magnetic field to neutralize the static charge on the particulates and facilitate the removal of the contaminants from the material. The flow of contaminant laden air is discharged from the deduster, while the cleaned particulate material is passed on to the manufacturing process.
A compact dedusting apparatus is disclosed in U.S. Pat. No. 6,595,369, granted on Jul. 22, 2003, to Jerome I. Paulson. Like the larger dedusting apparatus depicted in U.S. Pat. No. 5,035,331, the follow of particulate material is cleansed of contaminates that have had the static charged attracting the contaminates to the particulates neutralized. The cleaning process utilizes a flow of air passing through the stream of particulate material passing over wash decks. The contaminate-laden air is discharged through the top of the dedusting apparatus, while the cleaned particulate material is discharged from the bottom of the deduster.
These compact dedusters are provided with single and double (back-to-back) wash decks and are utilized with a vertically oriented conduit in which particulate material is conveyed to the manufacturing apparatus utilizing the particulate material. Accordingly, the product inlet opening at the top of the dedusting apparatus is in vertical alignment with the cleaned product outlet opening. The particulate material is introduced into the inlet opening and is metered onto a diagonally oriented primary wash deck through which air is blown from an air supply inlet to clean dust and debris from the particulate material flowing over the wash deck. In these dedusting devices, the particulate material is discharged off the lower end of the wash deck and falls through a Venturi zone in which air is moving upwardly to provide a vigorous cleaning action to the particulate material. The material falling through the Venturi zone is received on a secondary wash deck that is oriented oppositely of the primary wash deck to direct material back to the centrally aligned cleaned product outlet opening.
Not all manufacturing facilities utilizing particulate material that needs to be cleaned from dust and debris before being subjected to a manufacturing process have an appropriately located vertical conduit through which the particulate material is being conveyed. Some manufacturing plants have multiple silos containing storage of particulate material with these silos feeding into a single loading device or a processing machine such as an extruder. Examples of such operations would be a bagging station, big bag loading, truck and railroad car loading facilities, which ultimately lead to a single loading spout from multiple sources. Such silo loading pipes are declined at an angle to horizontal, which in most cases is 60 degrees. The steep angle of 60 degrees is necessary for the good flow of the particulate material through the conduit. Installing a conventional dedusting apparatus having a vertically aligned product inlet and outlet openings to the diagonally oriented discharge conduit would require that the conduit be re-configured to make the conduit more horizontal than originally designed to accommodate the insertion of the vertically oriented dedusting apparatus. Such re-configuration of the product feed conduits can require a significant capital outlay and increase the cost of installation and operation of a dedusting apparatus. Also, in some situations, a conventional compact dedusting apparatus having the inlet and outlet ports vertically aligned are too large vertically to be utilized. Accordingly, a dedusting apparatus having a smaller height dimension would be desirable for use in such height restricted applications.
Accordingly, it would be desirable to provide a dedusting apparatus that can be inserted directly into a diagonally oriented product feed conduit without requiring a re-configuration of the conduit to incorporate a vertically oriented conduit section.
The wash decks in these compact dedusting devices are formed with holes and slots to permit the passage of air through the wash deck to effectively remove contaminates from the flow of particulate material flowing over the surface of the wash deck. Holes or apertures provide a defined stream of air upwardly through the wash deck. The slots are typically formed by slitting and depressing downwardly a portion of the material forming the surface of the wash deck to create a louver that will direct the flow of air upwardly along the surface of the wash deck in opposition to the direction of flow of the particulate material over the wash deck. The oppositely directed air flow from these louvers serves to provide turbulence in the generally laminar flow of particulate material, thus loosening and displacing the contaminates from the particulate material and enhancing the cleaning action of the dedusting apparatus.
It would also be desirable to provide a wash deck configuration that would enhance the cleaning operation of air being blown through a sloped wash deck to remove contaminates from particulate material flowing over the sloped wash deck.